This invention relates to an endoscope for image-observing or measuring an area filled with an opaque liquid. It has been known that an area filled with an opaque liquid such as a blood vessel or the internal wall of the heart of a living body may be observed by the use of an endoscope having a means for providing a field of vision by a transparent fluid.
FIG. 1 is a schematic view showing the principle of such an endoscope. In FIG. 1, 1 denotes a tube or catheter to be inserted into a living body, 2 denotes a blood vessel within the living body and 3 denotes an image fiber. Basically, the image fiber 3 is inserted into the catheter 1 and a transparent fluid is passed through the catheter 1 and is flushed into an observation area within the living body whereby the internal conditions of the body can be observed through the image fiber.
FIG. 2 shows one example of the leading end portion of the conventional endoscope provided with a transparent fluid flush means as a means for providing a field of vision. In FIG. 2, 3 denotes an image fiber for transmitting an image from the observation area to an optical system or measuring system not shown, 4 denotes a light guide for transmitting illumination light from a light source not shown to the observation area, 5 denotes a cylindrical lens set, 6 denotes a prism and 7, 8 denote advancing directions of transparent fluid and illumination light. The transparent material which may be a saline, is directly flushed from an outlet 9 into a blood vessel of a living body, for example, to dispel the blood from the observation area, whereby a transparent field of vision is formed in the blood vessel and the internal conditions of the blood vessel can be observed.
In this conventional endoscope shown in FIG. 2 , however, since the field of vision must be maintained in a condition which is free of blood and is transparent by continuously excluding the flow of blood, a constant flow of a great amount of transparent fluid, usually an amount substantially corresponding to the amount of fluid flow within the blood vessel, must continuously be supplied to the area during the observation operation. The endoscope adapted to be inserted into a living body for observation of the living body preferably has as small an outer diameter as possible. However, in the endoscope shown in FIG. 2, in order to supply the transparent fluid in a great amount as mentioned hereinabove, the outer diameter of the endoscope becomes of necessity rather large. In addition, the supply of the transparent fluid in a great amount also requires the use of a specific electrically driven power cylinder to increase the supplying pressure of the transparent fluid.
In order to supplement such defects of the conventional endoscope above stated, another type of endoscope having a transparent balloon as a means for providing a field of vision at the leading end thereof has been proposed and has become conventionally known.
FIGS. 3 and 4 show longitudinally sectional and end elevational views, respectively, of a conventional endoscope l0a with a transparent balloon.
In these FIGS., 3a denotes an image fiber, 5a denotes a lens, 4a denotes light guides, 7a denotes a transparent fluid transport passage, 9a denotes a fluid outlet, 11 denotes a transparent balloon and 12 denotes a sheath. The transparent balloon 11 is secured to the sheath 12 by adhesive and binding means (not shown). When the internal wall of the heart of a living body is observed, for example, by inserting the endoscope into the living body, a transparent fluid such as CO.sub.2 gas or a saline is passed through the transparent fluid transport passage 7a and discharged through the fluid outlet 9a to inflate the transparent balloon 11 at the leading end of the endoscope whereby a transparent field of vision is formed within the inflated transparent balloon 11.
FIG. 5 shows a conventional endoscope with a transparent balloon being used for the observation of the internal wall of the heart of a living body. The transparent balloon 11 inflated with the transparent fluid provides a transparent area 14 in contact with the heart's internal wall 13 between the endoscope and the heart's internal wall 13 whereby opaque blood 15 is excluded from the observation area to provide a field of vision for observation.
However, the above mentioned conventional endoscope with the transparent balloon has a small or insufficient support area for the large size of the transparent balloon 11 when inflated and, thus, has a low or insufficient support capacity for the balloon. For this reason, when the endoscope is inserted into a living body for the observation of the internal conditions of the living body, the inflated balloon 11 attached to the leading end of the endoscope sways at the joint between the endoscope body and balloon when subjected to a variation in the feed pressure of the transparent fluid and/or the reaction force from the living body tissue to be observed. Thus, the conventional endoscope with the transparent balloon has the disadvantage that the field of vision tends to be unstable during the observation operation. This sway of the balloon becomes greater when the thickness of balloon wall is made thinner in order to increase the transparency of the balloon.
FIGS. 6 and 7 show examples of the unstable conditions of the field of vision caused by the swaying of the inflated balloon at the joint between the endoscope body and balloon during the observation operation when subjected to outer force as shown by the arrows.